Polishing composition

Abstract

A polishing composition for a substrate for memory hard disk, comprising silica particles in an aqueous medium, wherein the silica particles satisfy a specified relationship between an average particle size of the silica particles on the number basis and a standard deviation on the number basis, wherein the average particle size is obtained by a determination by transmission electron microscope (TEM) observation, and wherein a particle size and a cumulative volume frequency in a range of particle sizes of from 60 to 120 nm satisfies a specified relationship; a method of reducing microwaviness of a substrate for memory hard disk, comprising the step of polishing the substrate for memory hard disk with the polishing composition; and a method for manufacturing a substrate for memory hard disk, comprising the step of polishing a Ni—P plated substrate for memory hard disk with the polishing composition. The method can be suitably used for the manufacture of a substrate for precision parts, such as a substrate for memory hard disk.

1. A polishing composition for a substrate for memory hard disk, comprising silica particles in an aqueous medium, wherein the silica particles satisfy a relationship between an average particle size (r) of the silica particles on the number basis and a standard deviation (σ) on the number basis of the following formula (1):
   σ≧0.3 ×r   (1)  
 
       wherein r is an average particle size (nm) of the silica particles on the number basis, and σ is a standard deviation (nm) on the number basis, wherein the average particle size is obtained by a determination by transmission electron microscope (TEM) observation, and wherein a relationship between a particle size (R) and a cumulative volume frequency (V) in a range of particle sizes of from 60 to 120 nm satisfies the following formulas (2) and (3):
     V ≧0.5 ×R   (2)  
     V ≦0.25 ×R +75  (3)  
 
       wherein R is a particle size (nm) of the silica particles, and V is a cumulative volume frequency (%) counted from a small particle size side of the silica particles. 
     
     
       2. The polishing composition according to  claim 1 , wherein the silica particles are colloidal silica particles. 
     
     
       3. The polishing composition according to  claim 1 , further comprising at least one member selected from the group consisting of acids, salts thereof and oxidizing agents. 
     
     
       4. The polishing composition according to  claim 2 , further comprising at least one member selected from the group consisting of acids, salts thereof and oxidizing agents. 
     
     
       5. The polishing composition according to  claim 1 , wherein a pH thereof is from 1 to 4.5. 
     
     
       6. The polishing composition according to  claim 2 , wherein a pH thereof is from 1 to 4.5. 
     
     
       7. The polishing composition according to  claim 3 , wherein a pH thereof is from 1 to 4.5. 
     
     
       8. The polishing composition according to  claim 4 , wherein a pH thereof is from 1 to 4.5. 
     
     
       9. A method of reducing microwaviness of a substrate for memory hard disk, comprising the step of polishing the substrate for memory hard disk with the polishing composition of  claim 1 . 
     
     
       10. A method of reducing microwaviness of a substrate for memory hard disk, comprising the step of polishing the substrate for memory hard disk with the polishing composition of  claim 2 . 
     
     
       11. A method of reducing microwaviness of a substrate for memory hard disk, comprising the step of polishing the substrate for memory hard disk with the polishing composition of  claim 3 . 
     
     
       12. A method of reducing microwaviness of a substrate for memory hard disk, comprising the step of polishing the substrate for memory hard disk with the polishing composition of  claim 4 . 
     
     
       13. A method of reducing microwaviness of a substrate for memory hard disk, comprising the step of polishing the substrate for memory hard disk with the polishing composition of  claim 5 . 
     
     
       14. A method of reducing microwaviness of a substrate for memory hard disk, comprising the step of polishing the substrate for memory hard disk with the polishing composition of  claim 6 . 
     
     
       15. A method for manufacturing a substrate for memory hard disk, comprising the step of polishing a Ni—P plated substrate for memory hard disk with the polishing composition of  claim 1 . 
     
     
       16. A method for manufacturing a substrate for memory hard disk, comprising the step of polishing a Ni—P plated substrate for memory hard disk with the polishing composition of  claim 2 . 
     
     
       17. A method for manufacturing a substrate for memory hard disk, comprising the step of polishing a Ni—P plated substrate for memory hard disk with the polishing composition of  claim 3 . 
     
     
       18. A method for manufacturing a substrate for memory hard disk, comprising the step of polishing a Ni—P plated substrate for memory hard disk with the polishing composition of  claim 4 . 
     
     
       19. A method for manufacturing a substrate for memory hard disk, comprising the step of polishing a Ni—P plated substrate for memory hard disk with the polishing composition of  claim 5 . 
     
     
       20. A method for manufacturing a substrate for memory hard disk, comprising the step of polishing a Ni—P plated substrate for memory hard disk with the polishing composition of  claim 6 .